1. Field of the Invention
The present invention relates to forming esters of carbohydrate materials.
2. Description of the Art Practices
It is desirable to form organic solvent-dispersible carbohydrates which have been esterified. Specifically, materials such as starch may be esterified, however, present routes are difficult to follow and therefore reduce the practicality of manufacturing such products.
It is suggested that the reader consult U.S. Pat. No. 4,060,506, Verbanac, issued Nov. 29, 1977, for a general discussion of water-dispersible, cross-linkable starches. The general preparation of starch acetates using acetic acid or acetic anhydride is described in Whistler Starch: Chemistry and Technology, Vol. II, Academic Press, New York, 1967, pp. 376-380. It is also suggested that R. W. Kerr, Chemistry and Industry of Starch, Second Ed., Academic Press, New York, 1950, pp. 262-293, be reviewed for its disclosures of starch esters.
It is desired that a starch not be fully esterified as the ester is quite stable. That is, the hydroxyl groups on the starch molecule will not be free, and a fully esterified starch is not useful in preparing reactive coatings. While the starch molecule could be esterified to a degree of substitution of 3 corresponding to each of the hydroxyl groups on the glucoside unit, such is not done. The term "glucoside" refers to the individual six-membered ring component within the starch (polymer) which has 3 hydroxyl groups available for esterification. It is desirable that the degree of substitution be less than 3 so that the starch will retain an active hydroxyl site for chemical reactions.
The use of perchloric acid or sulfuric acid as a catalyst to form starch esters is described in U.S. Pat. No. 2,399,455 issued Apr. 30, 1946 to Treadway. The use of phase transfer catalysis in the treatment of monosaccharides is described in an article by Iverson, found in Chem. Commun. 1979, Vol. 5. The alkylation of carboxylic acids by solid-liquid phase transfer catalysis for determination by gas chromatography is described by Arbin et al. in the J. Chromatogr., 1979, Vol 170(1), pp. 25-33.
The acylation of carbohydrates in a catalytic 2-phase system is described in an article by Szeja, Pol. J. Chem. 1980, Vol. 54(6), pp. 1301-4. The selective esterification of primary hydroxyl groups in sugars in a catalytic 2-phase system is further described in an article by Szeja at Pol. J. Chem. 1980, Vol. 54(6), pp. 1323-5.
To the extent that the foregoing is applicable to the present invention, the references are incorporated herein by reference. Throughout the specification and claims, percentages and ratios are by weight, pressures are in atmospheres, and temperatures are degrees Celsius unless otherwise indicated.